Cancer is the result of aberrant cell growth. In order to formulate therapies for the various forms of the disease, it is necessary to understand the molecular mechanisms that regulate cellular development. Arabidopsis thaliana its known to express homologs of oncoproteins; it is also a system amenable to genetic, molecular and biochemical analyses. Therefore, the study of signal transduction pathways in Arabidopsis will yield valuable information about normal cellular development. Organellar biogenesis requires the coordinate expression of nuclear and organelle genes. There is evidence in plants that a chloroplast signal controls the expression of a subset of nuclear genes that functions in photosynthesis. The nature of the signal, and the means by which it is relayed to the nucleus, are unknown chloroplast genomes. gun mutants inappropriately express photosynthesis-related nuclear when chloroplast development is inhibited. I am currently cloning the GUNI gene, and when it is cloned, will characterize the gene product and determine how it helps coordinated nuclear and organellar gene expression. I am also carrying out genetic studies of the gun mutants, and the determining the plastid- responsive cis-acting sequencing in nuclear genes. The results from these experiments will further our understanding of intracellular signal transduction pathways.